[121.03] Barometrically Challenged Molecular Clouds

M. Heyer, R. Snell (FCRAO/UMass), J. Carpenter (OVRO/Cal Tech)

Over 8400 molecular regions have been identified within the
FCRAO CO Survey of the Outer Galaxy as closed surfaces within the
l-b-VLSR data cube. Assuming kinematic distances and a constant
conversion factor between CO luminosity and molecular hydrogen mass,
we find that molecular regions with mass less than 10^3 M_ødot are
not in gravitational equilibrium. The required external pressure (P/k)
to bound these objects is 2\times10^4 cm^-3-K.
The measured frequency of thermal pressure fluctuations within
the atomic medium
with this amplitude or greater
is consistent with the surface density of molecular material relative to
HI in
the outer Galaxy. While globally, these clouds are not self gravitational,
localized regions within the clouds have evolved to form embedded
clusters of newborn stars.